How it works
The sash is hinged at one side and swings out on a crank, like a small door. When you wind it shut, the mechanism pulls the sash into the frame and compresses the weatherstripping the whole way around. That compression is why a casement holds air better than a window that slides past its seal.
Where it fits an Inland Empire home
A crank puts the sash where your arm cannot. Over a kitchen sink, above a run of counter, or high on a wall, a casement stays usable where a slider would not. In a narrow side yard you can angle the open sash into the breeze and scoop air into the room instead of watching it go past the house.
In bedrooms, a casement is often the window that opens beside a larger fixed pane, because the whole sash swings clear and meets the emergency escape minimum more comfortably than a narrow sliding sash of the same overall size.
What to watch for
The swing needs room. Before you put a casement over a walkway, a patio or a driveway, look at what an open sash would be standing in. On Inland Empire side yards this comes up more than people expect. Screens sit on the inside for the same reason, which surprises anyone coming from a slider.
The compression seal earns its keep in Climate Zone 10, where the air you paid to cool is worth keeping in the house. The glazing limits are the same either way, a U-factor at or below 0.30 and a solar heat gain coefficient at or below 0.23 on most jobs, but a tighter frame loses less around the glass on a 105 degree afternoon.
The crank is a mechanical part. It will want lubrication eventually and replacement someday. That is minor, but a fixed window has nothing to wear out and a casement does.